Linear actuator with position sensing system

ABSTRACT

An electromagnetic actuator assembly with a frame, a movable element, first and second sensor targets that are coupled to the movable element for movement therewith, first and second sensors that are coupled to the frame and a controller. The first sensor is configured to sense a position of the first sensor target and to produce a first sensor signal in response thereto. The second sensor is configured to sense a position of the second sensor target and to produce a second sensor signal in response thereto. The controller that receives the first and second sensor signals and identifies three or more discrete points along a path of travel of the plunger. A differential assembly that incorporates the electromagnetic actuator assembly is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 11/933,667 filedNov. 1, 2007, which claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/861,196 entitled “Linear Actuator With PositionSensing System” filed Nov. 27, 2006. Each of the aforementionedapplications are hereby incorporated by reference as if fully set forthin detail herein.

INTRODUCTION

The present disclosure generally relates to linear actuators, such as alinear actuator that can be employed to selectively lock a lockingdifferential. More particularly, the present disclosure relates tosensing systems for use in determining the state or position of a linearactuator.

U.S. patent application Ser. No. 11/507,311 entitled “ElectronicallyActuated Apparatus Using Solenoid Actuator With Integrated Sensor”discloses a device that includes an electrically activated solenoid anda sensing system that is integrated with the solenoid for sensing astate or position of a moving component of the solenoid, such as thearmature or the plunger. Many of the examples described and illustratedin the '311 patent application employ a single sensor, such as aHall-effect sensor, to determine a state or position of the movingcomponent of the solenoid. While such configurations are highlydesirable as they are both compact and relatively low-cost, we havenoted that there are some instances in which additional resolutionand/or redundancy would be desirable.

SUMMARY

In one form, the present teachings provide an electromagnetic actuatorassembly that includes a frame member, a coil assembly, a plunger, anarmature, first and second sensor targets, first and second sensors anda controller. The frame member has an outer sidewall, an inner sidewalland a first end wall that is coupled to the inner and outer sidewalls.The frame member defines an interior annular cavity. The coil assemblyis mounted in the annular cavity and includes a core and a coil. Theplunger has an annular intermediate wall and a second end wall thatextends radially inwardly from the intermediate wall. The intermediatewall is disposed between the coil assembly and the outer sidewall. Thearmature abuts the plunger. The first and second sensor targets arecoupled to the plunger for movement therewith. The first and secondsensors are mounted to the frame. The first sensor is configured tosense a position of the first sensor target and to produce a firstsensor signal in response thereto. The second sensor is configured tosense a position of the second sensor target and to produce a secondsensor signal in response thereto. The controller receives the first andsecond sensor signals and identifies three or more discrete points alonga path of travel of the plunger.

In another form, the present teachings provide a differential assemblywith a differential case, a gear set and a locking system. The gear setis received in the differential case and has a pair of side gears and apair of pinion gears that are meshingly engaged to the side gears. Thelocking system is configured to selectively lock one of the side gearsto the differential case. The locking system includes an electromagneticactuator assembly with a frame member, a coil assembly, a plunger, anarmature, first and second sensor targets, first and second sensors anda controller. The frame member has an outer sidewall, an inner sidewalland a first end wall that is coupled to the inner and outer sidewalls.The frame member defines an interior annular cavity. The coil assemblyis mounted in the annular cavity and includes a core and a coil. Theplunger has an annular intermediate wall and a second end wall thatextends radially inwardly from the intermediate wall. The intermediatewall is disposed between the coil assembly and the outer sidewall. Thearmature abuts the plunger. The first and second sensor targets arecoupled to the plunger for movement therewith. The first and secondsensors are mounted to the frame. The first sensor is configured tosense a position of the first sensor target and to produce a firstsensor signal in response thereto. The second sensor is configured tosense a position of the second sensor target and to produce a secondsensor signal in response thereto. The controller receives the first andsecond sensor signals and identifies three or more discrete points alonga path of travel of the plunger.

In yet another form, the present teachings provide an electromagneticactuator assembly that includes a frame member, a coil assembly, anarmature, first and second sensor targets, first and second sensors, anda controller. The coil assembly includes a core and a coil. An elementof the actuator assembly is movable in response to energization of thecoil from a first position to a second position. The first and secondsensor targets are coupled to the movable element. The first and secondsensors are mounted to the frame. The first sensor is configured tosense a position of the first sensor target and to produce a firstsensor signal in response thereto. The second sensor is configured tosense a position of the second sensor target and to produce a secondsensor signal in response thereto. The controller receives the first andsecond sensor signals and identifies three or more discrete points alonga path of travel of the movable member.

In still another form, the present teachings provide a differentialassembly with a differential case, a gear set and a locking system. Thegear set is received in the differential case and has a pair of sidegears and a pair of pinion gears that are meshingly engaged to the sidegears. The locking system includes a locking element and anelectromagnetic actuator assembly that is configured to move the lockingelement between a first position, which inhibits speed differentiationbetween the side gears, and a second position that permits speeddifferentiation between the side gears. The electromagnetic actuatorincludes a frame member, a coil assembly, an armature, first and secondsensor targets, first and second sensors and a controller. The coilassembly is mounted in the frame member and includes a core and a coil.An element of the actuator assembly is movable in response toenergization of the coil from a first position to a second position. Thefirst and second sensor targets are coupled to the movable element formovement therewith. The first and second sensors are mounted to theframe. The first sensor is configured to sense a position of the firstsensor target and to produce a first sensor signal in response thereto.The second sensor is configured to sense a position of the second sensortarget and to produce a second sensor signal in response thereto. Thecontroller receives the first and second sensor signals and identifiesthree or more discrete points along a path of travel of the movableelement.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is an exploded perspective view of an actuating deviceconstructed in accordance with the teachings of the present disclosure,the actuating device being associated with a locking mechanism of anelectronic locking differential;

FIG. 2 is a cross-sectional view of a portion of the actuating device ofFIG. 1;

FIG. 3 is a perspective view of a portion of the actuating device ofFIG. 1 illustrating the plunger of the solenoid in more detail;

FIG. 4 is a perspective view of a portion of the actuating device ofFIG. 1;

FIG. 5 is a plot showing an engaged or disengaged condition of a familyof electronic locking differential assemblies as a function of thedistance with which a plunger has traveled;

FIG. 6 is a plot illustrating the output of the sensing system as afunction of the distance with which the plunger has traveled; and

FIGS. 7 through 9 are schematic illustrations of other sensing systemsconstructed in accordance with the teachings of the present disclosure.

DETAILED DESCRIPTION OF THE VARIOUS EMBODIMENTS

With reference to FIGS. 1 and 2 of the drawings, an actuating deviceconstructed in accordance with the teachings of the present invention isgenerally indicated by reference numeral 10. The actuating device 10 caninclude a solenoid 12 and a sensing system 14. The solenoid 12 can beconstructed in a manner that is similar to that which is described inU.S. patent application Ser. No. 11/507,311 entitled “ElectronicallyActuated Apparatus Using Solenoid Actuator With Integrated Sensor”,filed Aug. 21, 2006, the disclosure of which is hereby incorporated byreference as if fully set forth in detail herein. Briefly, the solenoid12 can include a frame 20, a coil assembly 22, an armature 24 and aplunger 26. The coil assembly 22 can be selectively activated togenerate a magnetic field that can repel the armature 24 away from thecoil assembly 22 to thereby translate the plunger 26.

In the particular example provided, the actuating device 10 isassociated with an electronically locking differential 198 of the typethat is disclosed in the '311 patent application. Briefly, thedifferential 198 can include a differential case 200, a gear set 202,which can include a pair of side gears 204 and a pair of pinion gears206, and a locking system 208. The gear set 202 can be mounted in thedifferential case 200 such that the pinion gears 206 meshingly engagethe side gears 204. The locking system 208 can include a first dog ring212, which can be integrally formed with one of the side gears 204, asecond dog ring 214, which can be non-rotatably but axially movablymounted in the differential case 200, a return spring 216, a spacer ring218, a thrust plate 220, the solenoid 12 and a retaining ring 222. Thefirst dog ring 212 can include teeth 230 that can be meshingly engagedto teeth 232 on the second dog ring 214. The return spring 216 can biasthe second dog ring 214 away from the first dog ring 212 so that theteeth 230 and 232 are not engaged to one another. The spacer ring 218can be disposed between the differential case 200 and the second dogring 214. The thrust plate 220, the solenoid 12 and the retaining ring222 can be mounted on the differential case 200; the retaining ring 222can inhibit the removal of the thrust plate 220 and the solenoid 12 fromthe differential case 200. The solenoid 12 can be operated to drive thethrust plate 220 away from the retaining ring 222 so that legs 238formed on the thrust plate 220 move the spacer ring 218 (andconsequently the second dog ring 214) toward the first dog ring 212 tocause the teeth 232 of the second dog ring 214 to meshingly engage theteeth 230 of the first dog ring 212 to thereby lock the differential198.

With reference to FIGS. 1, 3 and 4, the sensing system 14 can include atarget mount 40, a first target 42, a second target 44, a first sensor46 and a second sensor 48. The target mount 40 can be coupled to orintegrally formed with a moving component of the solenoid 12, such asthe plunger 26. In the particular example provided, the target mount 40is formed in the side wall or rim member 50 of the plunger 26 and cancomprise one or more tabs 52 that can be sheared and bent outwardly fromthe rim member 50. Each tab 52 can define one or more apertures 54 intowhich the first and second sensor targets 42 and 44 can be received. Thefirst and second sensor targets 42 and 44 can be coupled to the tab(s)52 in any appropriate manner, including brazing and adhesives. The firstand second sensors 46 and 48 can be any appropriate type of sensor, suchas Hall-effect sensors (e.g., a programmable A1182 sensor marketed byAllegro MicroSystems, Inc. of Worchester, Mass.). The first and secondsensors 46 and 48 can be mounted to a stationary portion of the solenoid12, such as the frame 20. The first and second sensors 46 and 48 aredisposed on opposite sides of the target mount 40, but it will beappreciated that the first and second sensors 46 and 48 could be mountedon the same side of the target mount 40. In the particular exampleprovided, the first and second sensor targets 42 and 44 are positionedsuch that they are radially offset from one another relative to acenterline of the solenoid 12. It will be appreciated that the first andsecond sensors 46 and 48 are also positioned in a radially offset mannerthat corresponds to that of the first and second sensor targets 42 and44, respectively.

A plot illustrating a condition of a locking mechanism for a family ofelectronic locking differential assemblies as a function of a position(x) of the plunger 26 (FIG. 3) is shown in FIG. 5. The electroniclocking differential assemblies can be of the type that is illustratedand described in the aforementioned patent application and theircomponents are selected to either maximize or minimize the magnitude ofthe position (x) at which a change in the state of the electroniclocking differential occurs. For example, one set of components can beselected such that the magnitude of the positions at which theelectronic locking differential transitions out of a completelydisengaged condition (i.e., position x_(a)) and into a completelyengaged condition (i.e., position x_(y)) are relatively small, whileanother set of components can be selected such that the magnitude of thepositions at which the electric locking differential transitions out ofa completely disengaged condition (i.e., position x_(b)) and into acompletely engaged condition (i.e., position x_(z)) are relativelylarge. Those of skill in the art will appreciate that the components are“in tolerance” components and are selected to establish the end pointsof a first range of positions 70 in which all members of the family ofelectronic locking differential will be in a completely disengagedcondition, as well as the end points of a second range of positions 72in which all members of the family of electronic locking differentialswill be in a completely engaged condition. The components that can beemployed to establish the end points of the first and second ranges 70and 72 can be selected on the basis of extremes in tolerance ranges(e.g., maximum material condition or minimum material condition;extremes of the tolerances for flatness, parallelness and runout).

Given the data of FIG. 5, the first and second sensors 46 and 48 of FIG.4 can be programmed to produce the output that is illustrated in FIG. 6.The plot 74 illustrates the output of the first sensor 46 (FIG. 4) andas shown, transitions from a first signal (e.g., voltage) at positionx_(a) to a second signal (e.g., voltage) that is maintained as theposition (x) increases in magnitude. Similarly, the plot 76 illustratesthe output of the second sensor 48 (FIG. 4) and as shown, transitionsfrom a second signal (e.g., voltage) at position x_(a) to a first signal(e.g., voltage) that is maintained as the position (x) increases inmagnitude. It will be appreciated that with the first and second sensors46 and 48 (FIG. 4) thus calibrated, it is possible to identify when anelectronic locking differential assembly is operating in a disengagedstate and an engaged state without calibrating the first and secondsensors 46 and 48 (FIG. 4) to a given family member (i.e., withoutcalibrating to a given combination or specific set of in-tolerancecomponents).

While the sensing system 14 has been illustrated and described thus faras including one or more Hall-effect sensors, it will be appreciatedthat the invention, in its broadest aspects, can be constructed somewhatdifferently. For example, the sensing system 14 a can include one ormore magneto-resistive sensors as shown in FIG. 7. Each portion 80 ofthe sensing system 14 a that is associated with a corresponding one ofthe magneto-resistive sensors R4 can further include a Wheatstone bridge82, a low-pass filter 84 and a comparator 86.

The Wheatstone bridge 82 can include a first resistor R1, a secondresistor R2, a third resistor R3 and an associated one of themagneto-resistive sensors R4. As will be appreciated by those of skillin the art, the resistance of the magneto-resistive sensor R4 will varybased on the position of the magneto-resistive sensor R4 relative to amagnetic target that can be associated with the plunger 26 (FIG. 2). Theoutput of the Wheatstone bridge 82 can be processed through the low-passfilter 84 and input to the comparator 86, which can compare the outputto one or more control signals that can be produced by a resistor bank88, which can include a thermistor 90 and one or more resistors, such asresistors 92 a, 92 b, 92 c and 92 d. The thermistor 90 can be in closethermal proximity to the solenoid 12 (FIG. 1) and as such, can output asignal that is indicative of a temperature of the solenoid 12 (FIG. 1).The resistors 92 a, 92 b, 92 c and 92 d can be employed to identifydiscrete points along the path that the plunger 26 can travel. Forexample, if the sensing system 14 a is part of an actuating device thatis employed in a locking differential assembly of the type describedabove, the resistors 92 a, 92 b, 92 c and 92 d can be associated withpoints at which the locking system is always disengaged. It will beappreciated that the other portion of the sensing system 14 can besimilarly configured and that the resistors of a resistor bankassociated with its comparator can be associated with points at whichthe locking system is always engaged. It will further be appreciatedthat the sensing system could comprise a single magneto-resistive sensorand could employ a comparator with a resistor bank having one or moreresistors that are associated with points at which the locking system isalways disengaged and one or more resistors that are associated withpoints at which the locking system is always engaged. The comparator 86can output a signal that can be indicative of a position of the plunger.

The switching system 14 b of FIG. 8 is generally similar to theswitching system 14 a of FIG. 7, except that a controller ormicroprocessor 100 has been substituted for the comparators 86 and theresistor banks 88. In this regard, the functions of the comparators 86and the resistor banks 88 are performed by the microprocessor 100 andthe microprocessor 100 can output signals that are indicative of aposition of the plunger.

In the example of FIG. 9, the sensing system 14 c can be generallysimilar to the sensing system 14 a and 14 b of FIGS. 7 and 8,respectively, except that the first and second sensors 46 c and 48 c canbe configured with reverse polarity (i.e., the signal output from thefirst sensor 46 c is the inverse of the signal that is output from thesecond sensor 48 c). Configuration in this manner provides opportunitiesfor fault detection (e.g., short-to-ground condition or short-to-voltageinput condition). Additionally the first and second sensors 46 c and 48c can be commercially available magnetoresistive sensors that can beconfigured to sense a change in an angle of an applied magnetic field.In the example provided, the solenoid 12 c has a relatively short strokeand consequently, the first and second sensors 46 c and 48 c can beemployed to accurately approximate the linear distance that the firstand second targets 42 and 44, respectively, travel.

While specific examples have been described in the specification andillustrated in the drawings, it will be understood by those of ordinaryskill in the art that various changes may be made and equivalents may besubstituted for elements thereof without departing from the scope of thepresent disclosure as defined in the claims. Furthermore, the mixing andmatching of features, elements and/or functions between various examplesis expressly contemplated herein so that one of ordinary skill in theart would appreciate from this disclosure that features, elements and/orfunctions of one example may be incorporated into another example asappropriate, unless described otherwise, above. Moreover, manymodifications may be made to adapt a particular situation or material tothe teachings of the present disclosure without departing from theessential scope thereof. Therefore, it is intended that the presentdisclosure not be limited to the particular examples illustrated by thedrawings and described in the specification as the best mode presentlycontemplated for carrying out the teachings of the present disclosure,but that the scope of the present disclosure will include anyembodiments falling within the foregoing description and the appendedclaims.

1. An electromagnetic actuator assembly comprising a frame member, acoil assembly, an armature, first and second sensor targets, first andsecond sensors, and a controller, the coil assembly including a core anda coil, wherein an element of the actuator assembly is movable from afirst position to a second position in response to energizing the coil,the first and second sensor targets being coupled to the movableelement, the first and second sensors being mounted to the frame, thefirst sensor being configured to sense a position of the first sensortarget and to produce a first sensor signal in response thereto, thesecond sensor being configured to sense a position of the second sensortarget and to produce a second sensor signal in response thereto, thecontroller receiving the first and second sensor signals and identifyingthree or more discrete points along a path of travel of the movablemember.
 2. The electromagnetic actuator assembly of claim 1, wherein thefirst sensor target is mounted parallel to and circumferentially spacedfrom the second sensor target and wherein the first and second sensorsare circumferentially spaced from the first and second sensor targets,respectfully.
 3. The electromagnetic actuator assembly of claim 2,wherein the first and second sensors are magnetoresistive sensors. 4.The electromagnetic actuator assembly of claim 1, wherein the firstsensor has a polarity that is opposite a polarity of the second sensor.5. The electromagnetic actuator assembly of claim 1, wherein thecontroller includes a first resistor bank, a first comparator, a secondresistor bank and a second comparator, wherein the first comparatorcompares the first sensor signal to an output of the first resistor bankand wherein the second comparator compares the second sensor signal toan output of the second resistor bank.
 6. The electromagnetic actuatorassembly of claim 5, wherein the controller further includes atemperature sensor for sensing a temperature of the electromagneticactuator assembly.
 7. The electromagnetic actuator assembly of claim 1,wherein the controller includes a microprocessor for determining aposition of the movable element based on the first and second sensorsignals.
 8. The electromagnetic actuator assembly of claim 1, whereinthe first sensor is configured to sense an angular position of the firstsensor target.
 9. The electromagnetic actuator assembly of claim 1,wherein the movable element is the armature.
 10. A differential assemblycomprising: a differential case; a gear set received in the differentialcase and having a pair of side gears and a pair of pinion gears that aremeshingly engaged to the side gears; and a locking system comprising alocking element and an electromagnetic actuator assembly that isconfigured to move the locking element between a first position, whichinhibits speed differentiation between the side gears, and a secondposition that permits speed differentiation between the side gears, theelectromagnetic actuator comprising a frame member, a coil assembly, anarmature, first and second sensor targets, first and second sensors anda controller, the coil assembly being mounted in the frame member andincluding a core and a coil, wherein an element of the actuator assemblyis movable from a first position to a second position in response toapplication of energy to the coil to operate the coil, the first andsecond sensor targets being coupled to the movable element for movementtherewith, the first and second sensors being mounted to the frame, thefirst sensor being configured to sense a position of the first sensortarget and to produce a first sensor signal in response thereto, thesecond sensor being configured to sense a position of the second sensortarget and to produce a second sensor signal in response thereto, thecontroller receiving the first and second sensor signals and identifyingthree or more discrete points along a path of travel of the movableelement.
 11. The differential assembly of claim 10, wherein the lockingelement is a first dog ring and wherein the locking system furtherincludes a second dog ring, a return spring, and a thrust plate, thesecond dog ring being coupled to one of the side gears, the first dogring being non-rotatably received in the differential case, the returnspring biasing the first dog ring apart from the second dog ring, thethrust plate and the electromagnetic actuator assembly being mounted onthe differential case, the electromagnetic actuator assembly beingselectively actuatable to move the thrust plate to cause the first dogring to non-rotatably engage the second dog ring.
 12. The differentialassembly of claim 10, wherein the first sensor target is mountedparallel to and circumferentially spaced from the second sensor targetand wherein the first and second sensors are circumferentially spacedfrom the first and second sensor targets, respectfully.
 13. Thedifferential assembly of claim 12, wherein the first and second sensorsare magnetoresistive sensors.
 14. The differential assembly of claim 10,wherein the first sensor has a polarity that is opposite a polarity ofthe second sensor.
 15. The differential assembly of claim 10, whereinthe controller includes a first resistor bank, a first comparator, asecond resistor bank and a second comparator, wherein the firstcomparator compares the first sensor signal to an output of the firstresistor bank and wherein the second comparator compares the secondsensor signal to an output of the second resistor bank.
 16. Thedifferential assembly of claim 15, wherein the controller furtherincludes a temperature sensor for sensing a temperature of theelectromagnetic actuator assembly.
 17. The differential assembly ofclaim 10, wherein the controller includes a microprocessor fordetermining a position of the movable element based on the first andsecond sensor signals.
 18. The differential assembly of claim 10,wherein the first sensor is configured to sense an angular position ofthe first sensor target.
 19. The electromagnetic actuator assembly ofclaim 10 wherein the movable element is the armature.
 20. A differentialassembly comprising: a differential case; a gear set received in thedifferential case and having a pair of side gears and a pair of piniongears that are meshingly engaged to the side gears; and a locking systemfor locking one of the side gears to the differential case, the lockingsystem including a first dog ring, a second dog ring, a return spring,and a thrust plate and an electromagnetic actuator assembly, the firstdog ring being coupled to one of the side gears, the second dog ringbeing non-rotatably but axially-movably received in the differentialcase, the return spring biasing the second dog ring apart from the firstdog ring, the thrust plate and the electromagnetic actuator assemblybeing mounted on the differential case, the electromagnetic actuatorassembly being selectively actuatable to move the thrust plate to causethe second dog ring to non-rotatably engage the first dog ring, theelectromagnetic actuator assembly including a frame member, a coilassembly, an armature, first and second sensor targets, first and secondsensors and a controller, the coil assembly including a core and a coil,the first and second sensor targets being coupled to one of the coilassembly and the armature for movement therewith, the first and secondsensors being mounted to the frame, the first sensor being configured tosense a position of the first sensor target and to produce a firstsensor signal in response thereto, the second sensor being configured tosense a position of the second sensor target and to produce a secondsensor signal in response thereto, the controller receiving the firstand second sensor signals and identifying three or more discrete pointsalong a path of travel of thethe one of the coil assembly and thearmature; wherein the first sensor target is mounted parallel to andcircumferentially spaced from the second sensor target and wherein thefirst and second sensors are circumferentially spaced from the first andsecond sensor targets, respectfully. wherein the first and secondsensors are magnetoresistive sensors; wherein the first sensor has apolarity that is opposite a polarity of the second sensor; wherein thecontroller includes a first resistor bank, a first comparator, a secondresistor bank and a second comparator, wherein the first comparatorcompares the first sensor signal to an output of the first resistor bankand wherein the second comparator compares the second sensor signal toan output of the second resistor bank; wherein the controller furtherincludes a temperature sensor for sensing a temperature of theelectromagnetic actuator assembly; and wherein the first sensor isconfigured to sense an angular position of the first sensor target.